Application of combined drought index to assess meteorological drought in the south western region of Bangladesh

The southwestern region is one of the vulnerable areas of Bangladesh of drought. This study was conducted to determine the frequency and intensity of meteorological droughts in the southwestern region of Bangladesh using rainfall, temperature and groundwater data covering a period of 1994-2018. The Combined Drought Index (CDI) value is used for drought assessment and a Microsoft Excel-based CDI software package is deployed in calculating that. This software requires minimum two climatic variables among the rainfall, temperature and soil moisture data while rainfall data is mandatory. Here, rainfall and temperature data are used for soil moisture data are unavailable. Moreover, groundwater level data are analyzed to assess the impacts of drought on it. Spatio-temporal distribution of drought is shown using the ArcGIS tools. The result shows that drought is a common and recurrent feature for the southwestern region of Bangladesh. The monthly CDI analysis result shows that entire study period is experienced approximately 1%, 7%, 14% and 35% of extremely severe, severe, moderate and mild droughts, respectively. The yearly CDI index reveals that almost 60% of study period are affected by drought considering at least 6 months of the year are suffering from any form of drought. This phenomenon is high for last 10 years. Spatial and trend analysis shows that groundwater depth is getting lower and steeper in this region. So, all these indicate that south western region of Bangladesh is vulnerable to extreme drought, which is mostly appearing during the pre-monsoon (February-May) period of the twelvemonth.